Compressing protocol headers has traditionally been attractive for conserving bandwidth over low-speed links, including those in wireless systems, by minimizing header overheads. Typically, the header overhead associated with the protocol stacks used is prohibitive on low-bit rate links, where compression down to a few dozen bytes per real-time information packet is often desirable. Generally, data link header compression reduces the size of a header at the data link layer of the protocol stack, while network layer header compression reduces the size of the header at the network layer of the protocol stack. One of the known schemes is the Van Jacobson TCP/IP header compression algorithm, which reduces the size of the TCP/IP headers to as few as three bytes. This can be a significant improvement on slow serial lines, particularly for interactive traffic, especially between devices with substantially limited computing power or having reduced bandwidth. This form of TCP/IP header compression is described in RFC 1144 (“Compressing TCP/IP Headers for Low-Speed Serial Links”). The protocol describes a maximal compression algorithm that relies on knowledge of the fields in the TCP/IP headers and how they are likely to change from packet to packet
The Van Jacobson compression of TCP/IP headers is usually negotiated during the establishment and configuration of the network layer protocol. However, on some operating systems, such as PALM® OS, it may not be feasible to intercept Internet protocol (IP) packets at the network layer, due to the system architecture.
However, this functionality can optionally be implemented in the Point-To-Point Protocol (PPP). This may be the case where a software module, such as a driver, is placed below the PPP layer to analyze or perform a certain operation on IP packets. One such operation may be implementation of IP Security Architecture (IPSec), which provides data confidentiality and authentication services to IP data packets. Therefore, the driver below the PPP layer needs to either examine or modify IP packets as they are passed to and from the PPP layer. However, since the driver cannot access the compression parameters inside the PPP layer, it is therefore is unable to translate compressed TCP/IP headers.
It is therefore an object of this invention to mitigate at least one of these disadvantages.